1. Field of the Invention
This invention relates to a magnetic bubble memory, and more particularly to improvements in a detector which detects magnetic bubbles in such magnetic bubble memory.
2. Description of the Prior Art
Magnetic bubbles have their utility noted in a mass memory, a shift register etc. Research and development are vigorously carried forward at present, and various magnetic bubble memory devices have already been put into practical use. In such magnetic bubble memory, it is the most fundamental function to detect the existence or non-existence of the magnetic bubble representing an information. Detectors for the detection variously contrived have been proposed. Nowadays, there is generally used a detection system in which the magnetic bubble is detected and transformed into an electric signal by a transformer exploiting the magnetoresistance effect, the electric signal being delivered as an output.
FIG. 1 shows only a portion of a detector 1 in the "major line--minor loops" organization which is one of typical magnetic bubble memory organizations. Referring to the figure, magnetic bubbles (not shown) on a read-out major line 2 are propagated in the direction of arrow 3 in accordance with a rotating magnetic field. Thus, they reach an inlet 4 of the detector 1. The magnetic bubble having reached the inlet 4 of the detector 1 is further propagated along arrow 3' within the detector 1 in accordance with the rotating magnetic field. Here, the detector 1 is constructed of a bubble expander 5 which propagates the magnetic bubble while gradually expanding it in the direction orthogonal to the propagating direction, a bubble detecting element 6 which is a magnetoresistive element that grasps as a change of its resistance value a change of a magnetic flux at the time when the expanded magnetic bubble passes therethrough, and a bubble sweeper 7 which receives the magnetic bubble from the bubble detecting element 6 and sweeps it into a bubble sink such as guardrail. Accordingly, the magnetic bubble having arrived at the inlet 4 of the detector 1 is propagated in the vertical direction within the bubble expander 5 in accordance with the rotating magnetic field and is simultaneously expanded in the lateral direction, and the magnetic bubble in the state in which it has been expanded most passes through the bubble detecting element 6 and is annihilated via the bubble sweeper 7. Typical patterns of the bubble expander 5, the bubble detecting element 6 and the bubble sweeper 7 which constitute the detector 1 are shown in FIG. 2 as an enlarged pattern of a part which is enclosed with a circle 8 indicated by a broken line. As apparent from FIG. 2, the patterns forming the respective portions are constructed of single Chevron pattern elements 9 which are made of a soft magnetic material such as permalloy. The bubble expander 5 is constructed of a large number of rows in which the stacked numbers of the single Chevron pattern elements 9 in the lateral direction (in the direction orthogonal to the propagating direction of the magnetic bubble) increase gradually from the inlet 4 to the bubble detecting element 6. The magnetoresistive element which forms the bubble detecting element 6 is represented as a single crooked long line in which the connection between the apices of the adjacent single Chevron pattern elements 9 and the connection between the ends on one side are alternately made. The bubble sweeper 7 is constructed of several rows in which the single Chevron pattern elements 9 are stacked in fixed numbers.
In case where the magnetic bubble memory is constructed by employing the typical magnetic bubble detector 1 as stated above, the widths .lambda. of the Chevron pattern elements 9 in the propagating direction 3' of the magnetic bubble are usually equal for all the bubble expander 5, the bubble detecting element 6 and the bubble sweeper 7. The width .lambda. is set to be several times the diameter of the magnetic bubble used. In this regard, it is a recent trend that the memory capacity per chip increases more and more. Therefore, the diameter of the magnetic bubble to be used diminishes, and the dimensions of the respective patterns constituting the magnetic bubble memory become small accordingly. The detector 1 needs to be similarly constructed in the smallest possible area, and the widths .lambda. of the Chevron pattern elements 9 to be used need to be also reduced.
However, in case where the widths .lambda. of the Chevron pattern elements 9 of the bubble expander 5, the bubble detecting element 6 and the bubble sweeper 7 constituting the detector 1 were narrowed at the same ratio, a problem to be stated below occurred. The magnetic bubbles are detected when they pass through the latter half part of the bubble detecting element 6. At this time, a great output fluctuation ascribable to the interference between the adjoining magnetic bubble arises, resulting in an erroneous detection. For the countermeasure against this drawback, a detecting electric circuit becomes very complicated. More specifically, the output of a detection signal of a magnetic bubble A in the case where magnetic bubbles lie successively as B, A and C as illustrated in FIG. 2 decreases about 30% in comparison with the output of the detection signal of the magnetic bubble A in the case where only the magnetic bubble A lies. Of course, also the output of the magnetic bubble A in the case where the magnetic bubbles are successive as B and A or as A and C decreases though the amount of the decrease is not so large as in the case described above. Such decrease of the detection output attributed to the interference between the magnetic bubbles is a very troublesome problem, and any countermeasure has been desired.